Transformer coupled plasmas are routinely used in a number of different applications including materials processing, production of activated gases, pollutant abatement and many others. In such devices, the magnetic core of the excitation transformer is placed in close proximity to, around or within a vacuum chamber. When the primary winding of this transformer is excited with radio frequency (RF), the electromagnetic fields induced around the core sustain a gas plasma discharge within the vacuum apparatus.
One of the main advantages of TCPs is that the power capacitively coupled into the plasma is minimized, resulting in a decrease in chamber wall damage through ion bombardment and, consequently, in extended lifetimes for the plasma chamber. However, this advantage poses a problem for plasma ignition since the capacitive fields are needed to start a plasma discharge.
One of the solutions to this problem has been the introduction of an auxiliary capacitive discharge used to generate enough free charges within the plasma chamber so that an inductively coupled plasma can be established. This additional capacitive discharge is usually driven by an external high voltage circuit.